The main idea is that all these scientists meeting and discussing will be able to find out hidden agendas, and let the science prevail. In the book 1 on science in the three tome IPCC reports, the scientists can only compile findings from research articles published in well known, internationally accepted scientific peer reviewed journals. This restricts the discussions fairly much in Working Group 1. The two other working groups are slightly less restricted.
However, in spite of meticulous control systems and vigorous debates on uncertainties and doubts, the reports should be read with a critical eye. Some skeptics argue that since the IPCC process demands consensus, the reports inevitably become conservative and avoid reporting the gloomy realities.
There are also some obvious, very powerful groups of 'deniers' who have vested economic interest in keeping fossil fuels as the main carriers of energy for as long as possible, especially under peak oil conditions. First of all the big multinational coal and oil companies.
Globally, the economical turnover of fossil fuel products adds up to tens or maybe hundreds of billions (thousand million) of dollars every day. The USA alone imports crude oil for USD two billion daily. Since the USA "produces" roughly half of its oil itself, it is safe to claim that the USA alone has a daily turnover of crude oil amounting to roughly USD 4 billion per day. The crude oil is refined to various petroleum products that are sold to much higher prices, on average probably two to five times as much.
In addition comes the coal, which amounts to about the same as the oil. It is fairly safe to claim that daily US turnover therefore runs up to more than USD 20 billion on fossil fuel products. Corresponding figues are found in Europe, China, India and elsewhere.
In addition the military-industrial complexes of the world have invested heavily in fossil fuel technology and are willing to go to great lengths to guard sources and pipelines. The arguments from these interest groups are often confounded with the more legitimate arguments from the sceptics. The main arguments are as follows: